Unbalanced Snow Load on Gable Roof (ASCE 7 7.6.1)
The ASCE 7-22 7.6.1 unbalanced gable case.
Example
You enter
- Ground snow load pg (psf) 30
- Balanced sloped-roof snow ps (psf) 25
- Roof slope (rise on 12) 4
- Eave-to-ridge length W (ft) 30
You get
- Windward slope load 7.5 psf
- Leeward peak (psf) 44.2
- Surcharge extent from ridge 8.6 ft
Details, formula, and sources
Windward slope drops to 0.3 ps while the leeward carries ps plus a wind-blown ridge drift surcharge (hd gamma/sqrt(S)). Applies only in the ~1/2:12 to 7:12 slope band with W > 20 ft; sizes the leeward rafter and ridge the balanced case misses.
gamma = min(0.13 pg + 14, 30); hd = 0.43 W^(1/3) (pg+10)^(1/4) - 1.5; windward = 0.3 ps; surcharge = hd gamma/sqrt(S) (S = 12/rise); leeward_peak = ps + surcharge; extent = 8 hd sqrt(S)/3.
The ASCE 7-22 Section 7.6.1 unbalanced snow load on gable/hip roofs, by name.
ASCE 7 is available through the ASCE Library at ascelibrary.org; the Chapter 7 snow provisions are public.
Estimate. AHJ and licensed professional govern.
Field names used by the API: ground_snow_pg_psf, flat_roof_ps_psf, roof_rise_on_12, eave_to_ridge_ft, windward_psf, leeward_peak_psf, extent_ft
- Applicability band slope ~2.38-30.2 deg (1/2:12 to 7:12) and W > 20 ft; outside it only the balanced load governsASCE 7-22 7.6.1
- Leeward surcharge ps + hd gamma/sqrt(S), tapering over 8 hd sqrt(S)/3 from the ridgeASCE 7-22 7.6.1